1. Field of the Invention
This invention relates to the preparation of alkyl tetrabromophthalates produced by the reaction of tetrabromophthalic anhydride with alkanols in the presence of titanium (IV) lower alkoxide catalyst.
2. Description of the Prior Art
The known synthesis of bis(2-ethyl-1-hexyl) tetrabromophthalate involves the reaction of tetrabromophthalic anhydride with 2-ethyl-1-hexanol in the presence of titanium (IV) isopropoxide as catalyst. However, the prior art processes for recovering the product have been unsatisfactory because of residual acidity in the reaction product and the presence of insoluble titanium catalyst residue. For example, Spatz, et al., "Discoloration of Tetrabromophthalic Anhydride Polyester Resins." I&EC Product Research and Development. Volume 8, December, 1969, pages 391, 395. describe two variations in the recovery of bis(2-ethyl-1-hexyl) tetrabromophthalate obtained by acid catalyzed esterification of tetrabromophthalic anhydride. The authors first suggest using low pressure distillation to recover the product after an elaborate purification by washing. Alternatively, the use of column chromotography is described. However. neither technique appears to be totally effective or commercially practicable.
Japanese Pat No. 50/5701. issued Mar. 6, 1975. describes a product purification approach involving the removal of excess alcohol in vacuo. followed by treatment of the crude ester with activated clay. Again, the reported results did not yield levels of satisfactory product quality.
U.S. Pat. No. 4,214.103 describes the purification of crude halogenated products. especially nuclear halogenated products produced by contacting an excess of bromine with the aromatic compound such as diphenyl ether in the presence of a bromination catalyst such as iron. aluminum and their halides. The described process comprises contacting the crude nuclear halogenated product with a finely divided basic solid such as a carbonate or bicarbonate of an alkali metal or ammonia in an organic solvent or in a molten state in the presence of a small amount of water. While the described process was successful in achieving its objectives. it did not deal with the problems posed by the recovery of bis(2-ethyl-1-hexyl) tetrabromophthalate, that is, the necessity of reducing residual acidity and removing titanium containing catalyst residue.
Accordingly. a primary object of the present invention is to provide a process for recovery of alkyl tetrabromophthalates.
A related object is to provide a method for recovery of bis(2-ethyl-1-hexyl) tetrabromophthalate produced by the reaction of tetrabromophthalic anhydride and 2-ethyl-1-hexanol in the presence of titanium isopropoxide catalyst.
A still further object is to provide a method of recovering bis(2-ethyl-1-hexyl) tetrabromophthalate which reduces residual acidity in the finished product to a very low level and which converts the titanium containing catalyst residue to a form that can be separated from the reaction product by filtration or other physical means.